Various types of mechanism have been proposed for devices for varying the valve property of the intake/exhaust valves of an internal combustion engine. For instance, JP2000-204917A and JP2011-185092A disclose valve rest mechanisms that can selectively prevent the operation of some of the valves.
According to a previous proposed valve rest mechanism, a valve lifter interposed between a drive cam and a valve is internally provided with a switch pin that can selectively move between the first position and a second position under oil pressure. At the first position, a stem end of the valve abuts an abutting surface defined on the switch pin so that the valve lifter is enabled to drive the valve into the open position when the valve lifter is actuated by the cam. At the second position, the stem end of the valve is received in a through hole formed in the switch pin so that the valve is kept in the closed position because the valve stem advances into the through hole without being pushed by the valve lifter even when the valve lifter is actuated by the cam.
In such a valve rest mechanism, the valve lifter has a circular cross section and is received in a support hole of the cylinder head having a corresponding cross section so that the valve lifter could rotate around the axial line thereof in the support hole. Therefore, to ensure supply of oil pressure into the chambers defined on either axial end of the switch pin, it is necessary to form circumferential oil grooves either on the outer circumferential surface of the valve lifter or the inner circumferential surface of the support hole that communicate with these chambers.
To overcome this problem, the valve lifter may be provided with a radially projecting pin that is engaged by a slot formed in the inner circumferential surface of the support hole. However, this requires extra component parts and machining of the cylinder head, and complicates the manufacturing process so that the manufacturing cost of the engine increases. Also, the frictional resistance to the movement of the valve lifter may be affected such an engagement feature.